Etching material



Patented June 10, 1941 2,245,219 n'ronmo MATERIAL Alexander Murray, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing.

Application April 27, 1940,

Serial No. 332,076

4 Claims.

This invention relates to etching material and particularly to etching materials used in engraving, such as those employed in photo-mechanical processes.

It is an object of the invention to provide a solution for etching zinc engravings.

It is a particular object of the invention to provide a solution which will result in sharply etched dots.

It is a particular object of the invention to give such a solution which renders these desired results even when used in a tray.

It is also an object of the invention to provide an etching solution which is non-gassing and is non-caustic and, hence, easy to use.

According to the invention, there is provided an etching solution containing copper sulphate, acid sodium sulphate, water, and a trace of material for reducing adhesion to the metal surface. Specifically, there is provided an etching solution containing between and 25 per cent by weight of copper salt, such as cuprio sulphate, between 1 and 3 per cent by weight of acid sodium sulphate, a trace of material for reducing adhesion to the metal and water.

I have found that the following forms an excellent etching solution which is particularly useful in schools, small newspaper work, and semi-amateur conditions in general.

CuSOmO solution per cent by weight Company, Inc., New York city) ..gm 0.005

On looking into the prior literature, I have noticed an old zinc etch as follows. CuSOr (2 parts) CuCl: (3 parts) water (64 parts) and HCl (8 parts). However, the concentration of the copper salts, about 6.5 per cent, is lower than I find to be economical. Also, there is a relatively large amount of acid of a caustic nature, and the solution gives oil large quantities of hydrogen gas in contact with the zinc. The results obtained with this material are inferior and it is diiiicult to use. Reference to this old zinc etch appears in Traite Pratique de Photogravure" by Leon Vidal, Paris, 1900, page 276, taken from Kruger, Die Zincogravure."

All prior methods including the one ust described fail to give a zinc etching with sharply etched dots and a smooth ground, in a tray. The almost universally used nitric acid etching solution requires elaborate arrangement for its I safe use. Cupric salts alone will etch zinc but the precipitating copper adheres firmly in places to the zinc.

The NaHSOr (acid sodium sulphate sometimes called sodium bisulphate) added according to the invention is an acid salt which has no caustic action on the skin, is very cheap when purchased in its crude form, namely niter cake. and can also be handled safely and conveniently in a dry state. Its solutions etch zinc slowly, evolving hydrogen gas, with the production of a rough ground.

Darvan is a proprietary material, similar to oxgall, that reduces the adhesion of the gas bubbles to the zinc, so that only small bubbles are formed which quickly detach themselves. That is, it changes the character of the hydrogen evolution in a zinc etch, producing very minute bubbles which do not remain adhering to the metal. It is effective in concentrations of the order of 5 parts in 100,000 as in the preferred example given above.

In my etching solutions, the quantityof acid sodium sulphate given produces an almost unnoticeable evolution of minute gas bubbles which prevent copper from adhering tightly to thezinc surface. The copper sulphate concentration is high enough to etch a newspaper halftone ina tray, with occasional brushing, in from 4 to 8 minutes. The result is as clean and sharp as machine etching.

The preferred example given above is quoted in amounts such as actually used. In terms of percentage of dry CuSOi and dry Nail-i804, the etching material should contain between 10 and 25% of copper salts (CuSOi is the preferable one) and between and 10% of NAHSOi.

Having thus described the preferred embodiment of my invention and the advantages thereof, I wish to point out that it is not limited to this embodiment but is of the scope of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

1. An etching solution containing about parts of a 20 per cent by weight cupric sulphate CuSO45H2O solution, 5 parts of a 35 per cent by weight niter cake solution, and a trace of material for reducing surface adhesion.

2. An etching solution containing between 10 and 25 per cent by weight of anhydrous copper salt, between and 10 per cent by weight of said sodium sulphate, a trace of material for reducing surface adhesion of gas and copper, and water.

3. An etching solution containing between 10 and 25 per cent by weight of CuSO4, about 2 per cent by weight of acid sodium sulphate, about .005 per cent of material for reducing surface adhesion of gas and copper and water.

4. An etching solution containing cupric sulphate, acid sodium sulphate, water, and a trace of material for reducing surface adhesion.

ALEXANDER MURRAY.

CERTIFICATE OF CORRECTION. Patent No. 2,215,219. June 10, 19m.

ALEXANDER MURRAY.

It is hereby certified that error appears in the. printed specification of the above numbered patent requiring correction as follows: Page 1, sec- 0nd column, line 148, claim 2, for the word "said" read -acid--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 2nd day of September, A. D. 191d.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents. 

